Pointed needles of medical devices, either hollow or solid represent a real hazard to health care workers. Besides causing puncture wounds which carry the risk of infection of skin and deeper structures such as the subcutaneous tissue, the fascia, the muscle and bone, they can transmit multisystem diseases to the health care workers victim of accidental exposure. Numerous are the diseases that have the potential to be transmitted via accidental sticks: hepatitis, malaria, syphilis and, the most frightening of all, AIDS. Risks of transmission are inherent to the medical profession and strict prevention guidelines cannot eliminate the hazards completely. The only successful way to avoid accidental exposure is to provide all the medical devices having pointed needles with protective mechanisms which safely shield the pointed needles from accidental exposures.
A search in the patent office has revealed numerous protective devices for the exposed needle tip of medical devices. Two are the basic mechanisms of protection applied to medical needles.
In one type of devices the needle is retracted and enclosed within a protective shield either manually or by resilient means.
In the other type of devices a protective sleeve or guard is advanced manually or by resilient means over the needle enclosing the needle as a whole or enclosing just the pointed tip. Various are the mechanisms described for achieving the locking of the sleeve or guard in respect to the needle and various are the needle tip shielding mechanisms in either group of devices.
While our search revealed many protecting mechanisms in which the needle guard is a part of the housing of the medical device to which the needle is applied to, or is simply connected to, we found only two patents, U.S. Pat. No.4,929,241 issued to John Kully and Patent Cooperation Treaty application No. PCT/CA 90/00031, published on Aug. 9, 1990 under International Publication No. WO 90/08564 issued to Inventor Robert Sircom, in which the protecting mechanism is a separated unit, i.e. with no attachment of any sort, from the medical device to which the needle is applied. In U.S. Pat. No.4,929,241 issued to Kully, a medical needle puncture guard is described in which a small protective guard slides over a medical needle. The front portion of the device comprises two jaws which collapse in front of the needle tip, once the needle tip is passed, to form a barrier in front of the needle tip. Arrest of the jaws in front of the needle tip is accomplished by two distinct mechanisms: anterograde arrest is accomplished by two opposing sharp blades projecting inward toward the needle shaft from the jaws, both obliquely and anteriorly oriented, exerting pressure on the needle shaft to the point of arresting its forward sliding motion impeding further advancement, once the transverse shields of the jaws have passed the needle tip.
Retrograde arrest is accomplished by the transverse barrier resulting from the collapsing of the transverse shields, as shown in FIG. 1, of the above cited U.S. Pat. No. 4,929,241 of the opposing jaws in front of the needle tip. The two jaws which collapse in front of the needle tip are each secured to mounting means. Collapse of the opposing jaws in front of the needle tip and arrest of the guard to forward motion by the opposing blades exerting arrest pressure over the needle shaft is necessarily accomplished by the resiliency of the jaws, said jaws urging opposed transverse shields 24 and 26 and opposed arresting blades to close on the needle shaft.
An unavoidable consequence of such concept is that the arrest to forward motion of the needle guard relies exclusively upon the degree of the pressure exerted by the opposing arresting blades upon the needle shaft, such degree of pressure on the needle shaft being dependent upon the degree of resiliency of the jaws to which said blades are secured. If such degree of resiliency is insufficient, then the needle guard will not arrest in proximity of the needle tip and the needle guard will inevitable fall off the needle defeating the purpose of the device, unless of course, modifications to the surface of the needles currently in the market are made, as for instance an arresting step, modifications which besides not being disclosed in such patent publication, do not appear to be reasonably practical.
The requirement for a resiliency of a sufficient degree to enable arrest to forward motion by the opposing arrest blades exerting pressure upon the needle shaft results in the drawback, inherent to the concept of the art disclosed by Kully, that also the transverse shields will inevitably be subjected to the same degree of resiliency which urges the opposing arresting blades to close together on the needle shaft because, alike arresting blades, transverse shields are secured to the same resilient jaws. As a result of the significant resiliency which transverse shields are subjected to while sliding forward along the needle shaft, the dynamic resistance and friction of the guard to forward sliding motion is also significant. In certain applications, such degree of friction is undesirable and in others it limits the usefulness of the device. More important than that, it appears that the needle guard disclosed by Kully does not guarantee an arrest to forward sliding motion of the guard, in fact, if the operator of the device advances the guard rapidly and forcefully, the guard may exit from the tip of the needle without arresting in proximity of the needle tip, unless the centripetal forces of the blades on the needle shaft is so impractically relevant to interfere with smooth and unopposed sliding of the guard over the needle. As a matter of fact, the arrest of the guard in the cited patent by Kully occurs as a probable event dependent upon the degree of centripetal force continuously exerted by the opposing blades during the slide motion of the guard on the needle shaft by resilient jaws.
Patent Cooperation Treaty application No. PCT/CA 90/00031, published on Aug. 9, 1990 under International Publication No. WO 90/08564 issued to Inventor Robert Sircom discloses a needle guard in which arrest to forward motion of the needle guard is accomplished by a locking plate having an orthogonally formed passageway for the needle shaft, said plate being orthogonally angled in respect to the longitudinal axis of the needle when being advanced along the needle, said orthogonally angled position being maintained by a sensing plate connected to the locking plate through an arm named canting lever. Contact of the sensing plate on the needle shaft is maintained by a spring arranged to secure such contact. Upon passage of the needle tip, the arm named canting lever, no longer retained in its position by the sensing plate sliding over the needle shaft, is driven further toward the needle by the spring causing canting of the locking plate in respect to the needle shaft. Said canting of the locking plate causes arrest of the plate by gripping exerted on the needle shaft by the sharp edges of the passageway formed in the locking plate in two points along the needle shaft in proximity of the tip opposite although not equidistant from the needle tip.
The locking mechanism of gripping type disclosed above provides a type of arrest of the needle guard on the needle shaft in proximity of the tip only in response to forward sliding motion of the guard over the needle. Backward sliding motion of the needle guard, i.e. withdrawal of the needle guard along the needle and exposure of the needle tip, is prevented, as in the case of Kully's patent, by the presence of a front plate, named sensing plate, collapsed just in front of the needle tip as in the Kully patent.
The presence of the spring disclosed by Sircom constitutes a significant drawback due to the friction caused by said spring urging the sensing plate against the needle shaft. As in the case of Kully's patent, such friction is constant regardless of the degree of force applied for forward sliding motion of the guard on the needle. Faster forward sliding motion will not increase the contact force and friction upon the needle shaft by the sensing means in either patent with resulting diminished reliability of the device in timely responding with self-arrest in proximity of the needle tip.
Our patent search has revealed that no known patent describes the mechanism of needle stick protection that we describe here in the present application.